Microstructure and plasmonic behavior of self-assembled silver nanoparticles and nanorings

Abstract

Self-assembled nanoparticles were formed after annealing ultrathin Ag films, which were grown on glass and quartz by direct current magnetron sputtering, in a furnace in air at 420 °C, 500 °C, or 600 °C. Intense localized surface plasmon resonances were observed for these samples in the entire range of visible light spectrum depending on the annealing time and nanoparticle size. Prolonged annealing resulted in the formation of nanorings and the change of the position and shape of resonances. The nanoring formation is attributed to partial evaporation of silver due to trapping of electromagnetic field by the larger nanoparticles despite the relatively low annealing temperature. Finally, in order to gain a further physical insight, the experimental results are compared with respect to rigorous theoretical calculations.

On the Localized Surface Plasmonic Resonances of AgPd Alloy Nanoparticles by Experiment and Theory

“…This may be interpreted after comparing these results to the ones of Ref. [23], where thicker Ag films after annealing resulted in larger NPs with red-shifted resonances. Two principal outcomes are stated: Firstly, the LSPRs are very broad compared to those of Ag NPs, see, e.g., Ref.…”

“…After evaluating the proper composition for LSPRs to be observed, for comparison reasons, we modified the deposition method by employing a cost-effective medium vacuum chamber with our sputter coater device (modified Balzers Union model SCD040, Oerlikon Balzers, Balzers, Liechtenstein) [23]. We directly fabricated the desired AgPd alloy film by co-deposition of Ag and Pd, implementing the same method applied for fabricating Cu and Au alloy films in Ref.…”

“…Spectra show only LSPRs and no sign of PdO. The thinner sample (trilayer) after annealing shows LSPRs with a peak close to the one of Ag NPs [23]. The thicker sample (five-layer) displays LSPRs red-shifted compared to the ones of the trilayer.…”

“…Two principal outcomes are stated: Firstly, the LSPRs are very broad compared to those of Ag NPs, see, e.g., Ref. [23]. However, this is not surprising if compared to the few literature data existing for AgPd NPs [10][11][12][13][14].…”

“…On the other hand, Pd gets gradually oxidized at temperatures above 300 • C approximately [21]. Since temperatures needed for obtaining self-organized NPs in air are higher than about 350 • C [22,23], it is important to keep oxidation of Pd at a minimal level. PdO is a semiconductor with an optical bandgap at about 2.2 eV [24].…”